Two-proton correlations near midrapidity in p+Pb and S+Pb collisions at the CERN SPS

Correlations of two protons emitted near midrapidity in p + Pb collisions a t 450 GeV/c and S + Pb collisions at 200 A GeV/c are presented, as measured by the NA44 Experiment. The correlation effect, which arises as a result o f final state interactions and Fermi-Dirac statistics, is related to the sp ace-time characteristics of proton emission. The measured source sizes are smaller than the size of the target lead nucleus but larger than the sizes of the projectiles. A dependence on the collision centrality is observed; t he source size increases with decreasing impact parameter. Proton source si zes near midrapidity appear to be smaller than those of pions in the same i nteractions. Quantitative agreement with the results of RQMD (v1.08) simula tions is found for p + Pb collisions. For S + Pb collisions the measured co rrelation effect is somewhat weaker than that predicted by the model simula tions, implying either a larger source size or larger contribution of proto ns from long-lived particle decays. (C) 1999 Published by Elsevier Science B.V. All rights reserved.